S/MIME Capabilities for Public Key Definitions
RFC 6664

Internet Engineering Task Force (IETF)                         J. Schaad
Request for Comments: 6664                       Soaring Hawk Consulting
Category: Informational                                        July 2012
ISSN: 2070-1721

             S/MIME Capabilities for Public Key Definitions

Abstract

   This document defines a set of Secure/Multipurpose Internet Mail
   Extensions (S/MIME) Capability types for ASN.1 encoding for the
   current set of public keys defined by the PKIX working group.  This
   facilitates the ability for a requester to specify information on the
   public keys and signature algorithms to be used in responses.
   "Online Certificate Status Protocol Algorithm Agility" (RFC 6277)
   details an example of where this is used.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6664.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Schaad                        Informational                     [Page 1]
RFC 6664           S/MIME Capabilities for Public Keys         July 2012

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1.  ASN.1 Notation . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Requirements Terminology . . . . . . . . . . . . . . . . .  4
   2.  RSA Public Keys  . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Generic RSA Public Keys  . . . . . . . . . . . . . . . . .  4
     2.2.  RSASSA-PSS Signature Public Keys . . . . . . . . . . . . .  5
     2.3.  RSAES-OAEP Key Transport Public Keys . . . . . . . . . . .  6
   3.  Diffie-Hellman Keys  . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  DSA Signature Public Key . . . . . . . . . . . . . . . . .  7
     3.2.  DH Key Agreement Keys  . . . . . . . . . . . . . . . . . .  8
   4.  Elliptic Curve Keys  . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Generic Elliptic Curve Keys  . . . . . . . . . . . . . . .  9
     4.2.  Elliptic Curve DH Keys . . . . . . . . . . . . . . . . . . 10
     4.3.  Elliptic Curve MQV Keys  . . . . . . . . . . . . . . . . . 10
   5.  RSASSA-PSS Signature Algorithm Capability  . . . . . . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   Appendix A.  2008 ASN.1 Module . . . . . . . . . . . . . . . . . . 15
   Appendix B.  1988 ASN.1 Module . . . . . . . . . . . . . . . . . . 18
   Appendix C.  Future Work . . . . . . . . . . . . . . . . . . . . . 19

1.  Introduction

   In the process of dealing with the Online Certificate Status Protocol
   (OCSP) agility issues in [RFC6277], it was noted that we really
   wanted to describe information to be used in selecting a public key,
   but we did not have any way of doing so.  This document fills that
   hole by defining a set of Secure/Multipurpose Internet Mail
   Extensions (S/MIME) Capability types for a small set of public key
   representations.

   S/MIME capabilities were originally defined in [SMIMEv3-MSG] as a way
   for the sender of an S/MIME message to tell the recipient of the
   message the set of encryption algorithms that were supported by the
   sender's system.  In the beginning, the focus was primarily on
   communicating the set of encryption algorithms that were supported by
   the sender.  Over time, it was expanded to allow for an S/MIME client
   to state that it supported new features such as the compression data